1. Field of the Invention
The present invention generally relates to a tandem rotary electric machine applicable to various applications, for example, movable bodies such as vehicles, and in particular relates to a tandem rotary electric machine in tandem mechanism having a single rotor shaft and plural pairs of a stator and a rotor, each of the stator rotor pair having a randel type rotor.
2. Description of the Related Art
There are well-known tandem rotary electric machines for vehicle or vehicle alternators capable of generating different voltages by stator-rotor pairs arranged in tandem mechanism and of outputting the different voltages to various electric loads. For example, two related-art documents have disclosed such a tandem rotary electric machine for vehicle, the Japanese patent laid open publication (Unexamined Published patent specification) No. JP-S56-112866 and the Japanese utility model laid open publication (Unexamined Published Utility model specification) No. JP-S57-42565. Those documents have shown a rotary machine for vehicle having a pair of randel-type rotors in tandem mechanism in order to increase the magnitude of output voltage.
Such a tandem rotary electric machine for vehicle is capable of controlling its electricity generation process to output different voltages independently, and is manufactured with a compact size at a relatively low manufacturing cost. Further, such a tandem rotary electric machine for vehicle can reduce its mount space in a vehicle when compared with a case in which two different non-tandem rotary electric machines are mounted separately on a vehicle.
Such a tandem rotary electric machine is applicable to vehicles having a double-voltage power system, for example, which is capable of supplying both a usual 12 volt power source as widely used and a 42 volt power source as a high voltage.
In the conventional tandem rotary electric machine having a double-voltage power supply system described above, a stator rotor pair of a high voltage side having a large rotational inertia mass is arranged at a pulley side, and on the contrary, a stator rotor pair of a low voltage side having a small rotational inertia mass is arranged at the opposite side to the pulley side because this has the most suitable arrangement in conventional design. However, the tandem rotary electric machine for vehicle having the above configuration involves following drawbacks.
In the conventional tandem rotary electric machine having a double-voltage power supply system described above, a low AC voltage generated by the low AC voltage generator is rectified by a rectifier and the rectified DC voltage is then charged into a battery. On the other hand, a high AC voltage generated by the high AC voltage generator needs no rectifier because those AC electric loads such as an electric pot and an electric heater incorporated in a vehicle use directly the high AC voltage that is not rectified.
By the way, because recent vehicles are equipped with high-voltage and high-power electric loads such as an electric power steering and an electric stabilizer that need and consume a direct current DC voltage, the use of such high-power electric loads needs a rectifier device for rectifying the high AC voltage to a high DC voltage, and further requires a mount space for the rectifier device on a vehicle, and still further requires a thermal protection for eliminating the heat generated by the rectifier device for rectifying the high AC voltage. That is, such a tandem rotary electric machine needs a plurality of rectifier components, each rectifier component is usually made of a junction diode, and the number of those rectifier components becomes twice or more of the number of rectifier components used in a usual non-tandem rotary electric machine. Therefore the tandem rotary electric machine requires a complicated and large thermal dissipation mechanism for those rectifier components, and thereby causes a difficulty of efficiently cooling the rectifier components forming the rectifier device.
For more details, the most important matter of the thermal dissipation mechanism for the rectifier device is to reduce the magnitude of heat resistance measured from each rectifier component to a low temperature heat source such as outside air, and to keep a heat sink function when the temperature of the rectifier device is greatly and rapidly increased on flowing a large amount temporal current through the rectifier components in the rectifier device. A weak heat sink capability of the thermal dissipation mechanism rapidly increases the temperature of the rectifier components when temporal current of large magnitude flows through the rectifier.
In general, the heat sink function means the connection between a heat source (such as rectifiers) and a heat accumulator with a large heat capacity and a small heat resistance. This heat accumulator is called the heat sink. In a conventional AC generator (or a rotary electric machine) for vehicle, each rectifier component forming a rectifier device is directly contacted to the outer surface of a rear housing or indirectly contacted to the surface of the rear housing through a good thermal conductive member, and the AC generator uses, as a heat sink, the rear housing or a stator core fixed to the rear housing. Hereinafter, this thermal dissipation mechanism will be referred to as “a rear housing mechanism with fixed rectifier component”. Accordingly, it is preferred for the tandem rotary electric machine for vehicle to have a thermal dissipation mechanism, namely, to have the rear housing mechanism with fixed rectifier components in the rectifier device.
However, as described above, because the tandem rotary electric machine for vehicle requires a plurality number of rectifier components in the rectifier device, the area for arranging each rectifier component reduces when compared with a usual non-tandem rotary machine. In other words, the total output power of and the total heat amount generated by the rectifier device in the tandem rotary electric machine become twice or more of those of the usual non-tandem rotary electric machine. Because the tandem rotary electric machine has a longer construction along its rotor shaft direction when compared with a usual non-tandem rotary electric machine, the area of the end face of the housing is little increased. That is, because the tandem rotary electric machine must have the total 12 rectifier components (24 rectifier components in a dual rectifier arrangement), that are twice of the usual non-tandem rotary electric machine, it is necessary to arrange and fix the rectifier components to the arrangement area of the end surface of the housing. This configuration reduces in half the capability of the heat sink (thermal absorption) of the housing and the stator core corresponding to each rectifier component.
Although it is possible to increase the size or thickness of the housing in order to enhance the heat sink capability of the rear housing mechanism with fixed rectifier component or the thermal dissipation mechanism, those manners are impractical because they also increase the entire size, volume, and weight of the tandem rotary electric machine.